The Anatomy of the Abdominal Aorta

The aorta is the largest blood vessel in the body. It is an artery, meaning that it carries blood away from the heart. The abdominal aorta enters the abdomen through the diaphragm at the level of the twelfth thoracic vertebre and continues to just below the umbilical area, where it splits into the right and left common iliac arteries. The aorta supplies oxygenated blood to most of the body.

Since so much blood flows through the aorta, it is an extremely sensitive blood vessel during trauma or certain types of medical conditions. If it is cut or ruptured, the aorta can lose the majority of the body's total blood volume in a few minutes, which can lead to death.

The aorta starts at the left ventricle of the heart and curves around toward the feet. The curve is known as the aortic arch. The entire aorta stretches from the thoracic cavity to the abdomen. All of the blood flow leaving the left ventricle flows through some or all of the aorta.

The area just above where the abdominal aorta bifurcates (divides into two branches) into the iliac arteries is susceptible to a weakening of the aortic wall called an abdominal aortic aneurysm. If diagnosed before a rupture occurs, an abdominal aortic aneurysm can be surgically repaired.

Anatomy

The descending aorta travels down the chest and becomes the abdominal aorta when it crosses the diaphragm, at about the twelfth thoracic vertebra. From there travels down to where it bifurcates into the left and right common iliac arteries.

Structure

By the time the aorta reaches the abdomen, it has tapered to a width of about 2 centimeters wide, making it the largest artery in the abdominal cavity. Like other blood vessels, the wall of the abdominal aorta is made up of three distinct tissue layers: the thin inner layer (tunica intima), the thick middle layer (tunica media), and the thin outer layer (tunica adventitia). that have the ability to constrict and relax as needed to adjust for high and low blood pressures.

Location

The abdominal aorta, which lies slightly left of the midline of the body, starts at the diaphragm and ends just above the pelvis. From there, it splits into two arteries, one for each leg. These are called the iliac arteries.

There are five arteries that branch off of the abdominal aorta:

• Celiac trunk supplies blood to the abdominal esophagus, stomach, liver, pancreas, gallbladder, and spleen
• Middle suprarenal arteries supply blood to the suprarenal glands that lie on top of the kidneys
• Superior mesenteric artery supplies blood to the small intestine
• Inferior mesenteric artery supply blood to the large intestine
• Median sacral artery supplies blood to the lumbar vertebrae and the sacrum
• Renal arteries provide blood to the kidneys
• Gondal (testicular and ovarian) arteries supply blood to either the testes in males or the ovaries in females
• Lumbar arteries supply blood to the posterior abdominal wall and the spinal cord
• Common iliac and its branches supply blood to the legs and the organs in the pelvis

Anatomical Variations

Variations in the abdominal aorta and its branches are very common and usually occur as a result of changes that occur during embryologic development. The arteries that show frequent variations include the celiac trunk, superior mesenteric artery, the renal artery, and the testicular arteries.

Function

As the largest blood vessel in the body, the aorta provides a conduit for all the blood flowing to the body from the heart other than the blood that flows to the heart itself. The abdominal aorta conducts blood to organs in the abdominal cavity as well as to the legs and feet. Also, the aorta helps to control blood pressure by dilating and constricting as necessary.

Clinical Significance

The most common condition to affect the abdominal aorta is an abdominal aortic aneurysm. An abdominal aortic aneurysm consists of a weakening of the wall of the aorta just above the point where it bifurcates into the left and right common iliac arteries. Abdominal aortic aneurysms are more common in men and among people aged 65 years and older.

The abdomen allows a lot of room for a weak aorta to expand and grow. It can develop a "bubble" of sorts, which can be compared visually to a snake that swallowed a rat—sort of bloated in one spot. Signs and symptoms of an abdominal aortic aneurysm are back pain, deep abdominal discomfort, and possibly a pulsating mass in the abdomen.

If a rupture occurs in the inside lining of the aorta, the tunica intima, it can lead to blood being forced between the tunica intima and the tunica media (the inside and middle layers of the aorta). Blood forced between them can lead to a separation of the two layers, known as a dissection. Dissections can also happen in the other parts of the aorta that live in the thoracic cavity (the chest), but abdominal aortic aneurysms are the most common.